刚google 了一下，刘全国的解释比较全

作主语：Seeing is believing.百闻不如一见。Talking is easier than doing. –ing作主语时，如果其结构较长，可用it作形式主语，而将作主语的-ing后置。如：It isn’t much good writing to them again. It’s no use waiting here.
-ing形式的复合结构。在-ing前加物主代词或名词所有格即构成-ing的复合结构。其中的物主代词或名词所有格为-ing的逻辑主语。这种结构在句中可作主语、宾语或表语，如：Your smoking and drinking too much will do harm to your health. 但在口语中，这种结构如作宾语用，其中的物主代词常用人称代词的宾格，名词的所有格常用名词的普通格代替，如：She insisted on Peter’s （or Peter）going there first.

所有跟帖： 

• you did not understand grep's question -justjust- ♂ (115 bytes) () 05/08/2009 postreply 20:09:55

• likely people would put -justjust- ♂ (33 bytes) () 05/08/2009 postreply 20:20:51

• I agree with you, just. this form can be a subject. -戏雨飞鹰- ♀ (0 bytes) () 05/08/2009 postreply 21:32:37

• I might have neglected that ... -billnet- ♂ (756 bytes) () 05/08/2009 postreply 21:57:21